I do not believe in asset allocation - but rather asset class rotation - to get the highest return within my own tolerance for risk. After I sold all common stocks last year, I sat in cash and then reinvested early Dec - all in preferred shares.
Most preferred owners are sold their positions from IPOs at face value. Those are a receipe for disaster. Buying them at a discount with an opportunity for capital gains due to projected drops in yields, is a good idea. A big problem with the ETF is that there is no way of knowing from their disclosure, what capital loss/gain you should include in your valuation. You don't know what the 'FaceValuePerUnit' is. Nor is there a 'YieldToPresumedCall' calculated. All you have to go on is the current yield - which tells you nothing.
A lot have now recovered to close to face value, so they have little upside left. But IMO the downside risk from common stocks far outweighs that little problem.
The ETF is certainly more liquid than individual issues. That can be quite important in certain circumstances, but I don't foresee those right now. Buying individual issues REQUIRES you to analyse the prospectus and appreciate what is there and NOT there.
Learn what to look for and how to predict the share's price at:
http://members.shaw.ca/retailinvestor/preferreds.html